Disilanes are useful base materials in photoresist compositions, ceramic precursor compositions, and electroconductive compositions, and particularly in photoresist compositions having oxygen plasma etching resistance.
In the prior art, disilanes are generally prepared through polycondensation of halosilanes in the presence of alkali metals such as lithium and sodium or reaction of halosilanes with alkali metal silicides such as silyllithium, provided that by-product disilanes formed during preparation of halosilanes by the direct process and derivatives thereof are excluded. These processes, however, involve hazards due to the use of alkali metals and are impossible, in principle, to produce disilanes having substituent groups capable of reacting with alkali metals.
It is also known to prepare disilanes by dehydrogenation condensation of hydrosilanes in the presence of noble metal catalysts. Being free from hazardous alkali metals, this process is of greater interest than the above halosilane processes. Rhodium, platinum, and iridium catalysts for use in such process are known from Organometallics, 6, 1590 (1987), Bull. Chem. Soc. Jpn., 68, 403, 1995, and J. Organomet. Chem., 593-594, 154, 2000, respectively. These catalysts are commercially less acceptable because of the expense of noble metals. Use of titanium catalysts is also reported in J. Organomet. Chem., 521, 145, 1996, J. Organomet. Chem., 279, C11, 1985, and Organosilicon Chemistry, VCH, Weinheim, p.253, 1994.
These prior art processes of forming Si—Si bonds through dehydrogenation condensation in the presence of noble metal catalysts or titanium catalysts start with dihydrosilanes or trihydrosilanes. Namely, the starting reactants must be silanes having at least two hydrogen atoms on a common silicon atom. For example, in the case of coupling of a primary or secondary silane with a lithium reagent such as BuLi in the presence of a titanium or Group 4 transition metal complex catalyst, a polysilane forms because a plurality of Si—H bonds are available as reaction sites. It is difficult to preferentially produce only the desired disilane.
The foregoing prior art processes fail to effect dehydrogenation condensation on monohydrosilanes, that is, silanes having one hydrogen atom on a silicon atom. Even when disilanes are produced, the amount of disilane produced does not exceed the amount of noble metal used as the catalyst. The processes are by no means economically acceptable.